NEWTOWN, Conn. (USA TODAY/WUSA)-- The head of the Connecticut Public Schools Superintendent's Association told CBS News that the mother of the gunman "had no relationship with the school."

The association also said that the victim's bodies have been identified and have been removed from the school, according to CBS News.

The elementary school shooting that left 20 children dead took place Friday morning in Newton, Ct. A lone gunman shot and killed his mother, then drove to a school and went on a shooting rampage Friday morning, killing 26 people in all, before turning a gun on himself.

The shooter was identified by the Associated Press as Adam Lanza, 20, who was found dead inside Sandy Hook Elementary School of a self-inflicted gunshot wound. Connecticut State Police says Lanza forced his way into the building, according to AP.

The incident -- among the worst school shootings in U.S. history -- is the latest in a series of mass shootings in the U.S. this year, including Tuesday's assault by a lone gunman at a Portland, Ore., shopping mall that left two dead and one wounded.

Three weapons were found - a Glock and a Sig Sauer, both pistols, inside the school, and a .223-caliber rifle in the back of a car.

USA TODAY's Kevin Johnson quoted a federal law enforcement official as saying the guns had been legally bought and registered by the shooter's 52-year-old mother, Nancy Lanza.

Ryan Lanza, the suspect's 24-year-old brother, was questioned by law enforcement in Hoboken, N.J., and said Adam was believed to suffer from a personality disorder. He told police that he had not been in touch with his brother since about 2010.

Restaurant owner Mark Tambascio, a family friend, said Nancy Lanza told him recently that her son Adam had Asperger syndrome, that he was "getting out of control and that she might need special help for him."

Tambascio told USA TODAY's Gary Stoller that Nancy was a good-hearted person who was "always doing something for some cause."

He also noted that she liked to target shoot, which could explain the guns registered in her name that were in Adam's possession.

Law enforcement officials speaking on condition of anonymity said Adam Lanza killed his mother early Friday, then drove to the school in her car with the three guns, walked into the building around 9:40 a.m. ET, shortly after classes began, and opened fire.

Police said the shootings took place in two rooms in one section of the school building, including a kindergarten classroom.

Theodore Varga said he was in a meeting with other fourth-grade teachers when he heard the gunfire, but there was no lock on the door.

He said someone turned on the public address system so that "you could hear the hysteria that was going on. I think whoever did that saved a lot of people. Everyone in the school was listening to the terror that was transpiring."

As the shooting erupted, quick-thinking teachers and faculty members hid some students in closets and bathrooms, while others rounded up students and spirited them out of the building.

Children lucky enough to escape the carnage fled in frightened groups -- some crying, some holding hands -- as they were escorted from the single-story school by teachers. Witnesses reported up to 100 shots were fired.

State Police Lt. Paul Vance said the murder scene was so gruesome that first responders, including tactical squad police, were provided counseling later in the day. "This was a tragic, horrific scene they encountered,'' he said.

Vance told reporters Friday night that the medical examiner and other officers were working through the night to identify the dead and to try to determined how the grim events unfolded. He said he hoped to release the names of the victims -- and the gunman -- on Saturday.

Vance said 18 of the children and six adults died at the school. Two other children were pronounced dead after they were taken to local hospitals. One wounded victim was hospitalized.

In Washington, a visibly shaken President Obama, wiping away tears, said he was "heartbroken."

"These were "beautiful little kids between the ages of 5 and 10 years old,'' Obama said. "They had their entire lives ahead of them. Birthdays. Graduations. Weddings. Kids of their own."

Sandy Hook is in a residential, wooded neighborhood about 60 miles northeast of New York City. The school, which serves kindergartners to fourth-graders, has 39 teachers and nearly 700 students. A reverse 911 call went out to parents warning of an incident, shaking the quiet, middle and upper-middle class community of 27,000 to its core.

"This is the most tragic thing we've ever encountered,'' said Newtown Police Lt. George Sinko. "We have to think about the families right now."

On Friday night, hundreds of people packed the St. Rose of Lima church in Newtown, a community of around 27,000 people, while hundreds more stood outside, to remember the victims. Some held hands in circles and offered prayers. Others lit candles and sang Silent Night.

In brief appearance Friday night, Gov. Dan Malloy described the youngest victims as "beautiful children who had simply come to school to learn."

On Friday afternoon, family members were led away from a firehouse that was being used as a staging area, some of them weeping. One man, wearing only a T-shirt without a jacket, put his arms around a woman as they walked down the middle of the street, oblivious to everything around them.

Another woman with tears rolling down her face walked by carrying a car seat with a young infant inside and a bag that appeared to have toys and stuffed animals.

Alexis Wasik, a third-grader at the school, said police were checking everybody inside the school before they were escorted to the firehouse. She said she heard shots and saw her former nursery school teacher being taken out of the building on a stretcher but didn't know if the woman had been shot.

"We had to walk with a partner," said Alexis, 8. One child leaving the school said that there was shattered glass everywhere. A police officer ran into the classroom and told them to run outside and keep going until they reached the firehouse, The Hartford Courant reported.

Counselors and crisis response staff from state mental health services, children and family services, public health and the Red Cross are working with federal and local officials on the scene, Gov. Dan Malloy's office said.

Children are likely to be traumatized, says Dr. Victor Fornari, director of Child/Adolescent Psychiatry at North Shore-LIJ Health System in New Hyde Park, NY. Schools are supposed to be safe, nurturing environment. The shooting shatters that belief. Listening to children and trying to be supportive and reassuring can be helpful, Fornari says.

James Alan Fox of Northeastern University's School of Criminology and Criminal Justice said Friday['s incident seems reminiscent of several from the late 1980s involving shooting rampages at schools.

Fox couldn't speak to the specifics of the Connecticut case, but said, "If someone is interested in punishing society where it's most vulnerable, they know that a school is a place where lots of young, innocent children, our most cherished members of society, are congregated and under their gun -- literally."

Children are often seen as "easy targets to get even with society - or maybe it was the school. We don't know what the primary target was, and the primary motive."

Still, over the past few years, shootings in K-12 schools have become increasingly rare. After reaching a high of 63 deaths in the 2006-2007 school year, the number of people killed in "school-associated" incidents dropped to 33 last year - lowest in two decades, according to the U.S. Department of Education.

While a few dozen children are killed each year in school, statistically speaking it remains the safest place a child will likely ever be, with the lowest chance of being killed. "When you consider the fact that there are over 50 million school children in America, the chances are over one in two million, not a high probability," said Fox. "And most cases that do occur are in high schools and less so in middle schools -- and hardly ever in elementary schools."